False Alarm Operation Resulting from Partial Wetting of High Voltage Outdoor Equipment

To achieve a high degree of safety and reliability of the outdoor high voltage equipment they must be automatically protected when a predetermined level of a neutral-to- ground voltage is exceeded. At a lower neutral-to- ground voltage difference than that employed to isolate the power system a warning signal gives a prior indication to the operator that the neutral-to- ground voltage is approaching the level of the automatic shutdown of the equipment. The warning signal voltage level (WSVL) iould be determined at the minimum permissible level without incurring unnecessary interruption of the power supply for all weather conditions. A method is reported which calculates the WSVL more reliably than in the past and takes into account a condition often present in bad weather namely a partial wetting of the high voltage equipment. The values of the WSVL obtained from the proposed method are in good agreement with those derived from field experiments.